The atomic force microscope (AFM) has become a standard instrument in nano-analysis with regards to the rapid and uncomplicated technical exploration of surfaces at the micro- and nanometre scales. During characterization, a probe mounted at the end of a cantilever beam is generally placed in direct contact with the sample, such that the surface topography is obtained through a raster scan while maintaining a constant tip-sample force. An important upgrade to this basic process is the so-called dynamic AFM mode, whereby the cantilever oscillates near the surface while changes in the oscillation amplitude are monitored while also recording the relative position of the tip and the sample. If one uses the amplitude change as the control signal, it is possible to measure the sample topography with high vertical and lateral resolution. This principle works in air, liquid and vacuum environments. Other techniques have also been developed to obtain information about the tip-sample interactions. For example, the resonant frequency of the cantilever can be measured as a function of the tip-sample separation, from which the tip-sample interaction force can be obtained (Hölscher et al., Phys. Rev. B 61, 12678 (2000)). However, these additional measurements can only be performed through a subsequent characterization after scanning of the surface topography.
The conventional techniques that are already established do not allow the simultaneous analysis of the tip-sample interactions during imaging of the surface.
The approach of Stark et al. [PNAS 99, 8473 (2002)] and Legleiter et al. [PNAS 103, 4813 (2006)] can in principle solve the problem through an elaborate analysis of the cantilever oscillation. However this is quite complex to perform and the noise is high.
The approach of Sahin et al. [Nature Nanotechnology 2, 507 (2007)] solves the problem through the use of special cantilevers. However these have the disadvantage of a coupling between the lateral and normal motion of the cantilever. Besides, the tip moves laterally in an undefined pattern and the lateral frequency of the tip is only slightly higher than the normal motion (typically below 20:1). The demands on the system electronics are so high that one can only use the specifically-designed, original electronics of the manufacturer Veeco Instruments, who have exclusively commercialized this technique under the name Harmonix (WO2006/014542 A1).
The manufacturing of miniature paddles is described in Evoy et al. [J. Appl. Phys. 86, 6072 (1999)] and Boonliang et al. [J. Micromech. Microeng. 18, 015021 (2008)]), the use of such paddles in cantilevers for AFM is not described.